Method and device for coating scaled forming products with a lubricant

ABSTRACT

A method and a device allow scaled strand-shaped metal forming products to be coated with a solid lubricant for the purpose of a forming process in a downstream drawing process while preventing the removal of scale layers present on the metal forming product or solid layers which contain scale. At the same time, the prerequisites for substantially improving the stability of the downstream drawing process and the quality of the produced products should be met. In the method, the scaled forming product is coated with a solid lubricant prior to the downstream drawing process and formed with a degree of deformation in excess of 3%. The forming product is then drawn through at least one accumulation chamber in order to mix the scale particles produced from the scale layer as a result of the forming process with the lubricant provided on the forming product after the forming process.

The invention relates to the field of metallurgy and relates to a method and an apparatus for coating of scale-covered, metallic, strand-shaped forming material with a lubricant, for forming during a downstream drawing process.

In the forming of scale-covered metallic strand-shaped forming material, the prior clearing process of the forming material, which is usually referred to as rolling wire, plays a significant role. It is generally known that rolling wire is covered with oxide layers, hydroxide layers, and scale layers or the like. These surface layers, which are primarily caused by the hot-forming process, must be carefully removed before drawing, because their presence not only brings about significantly greater wear of the drawing tools and a significant reduction in the possible drawing speed, but also results in a great quality reduction of the wire to be drawn. In many cases, a forming process is not even possible under such conditions.

A great number of methods is known for removal of such surface layers; these methods can essentially be divided into two groups, specifically the chemical and mechanical cleaning methods.

In the group of the chemical cleaning methods, wet pickling of the wire is fundamentally carried out, but a number of additional operations is required, such as, for example, neutralization, rinsing, drying, etc. Such method steps and the related devices are very cost-intensive. Furthermore, the media required for this purpose, such as acids and base, burden the environment to a not insignificant extent.

The mechanical cleaning methods can usually be divided into three cleaning ranges that follow one another in the drawing direction.

In the first cleaning range, the rolling wire is forced through a convoluted segment of two roll arrangements offset at an angle of 90°, in each instance, thereby bending the wire both alternately and in two planes rotated by 90°, and thereby causing the brittle scale layers to more or less flake off from the metal surface. Afterward, in every case, a second cleaning range is required, namely brushing with wire brush systems. Finally, the rolling wire is treated in a third cleaning range, to remove the oxide dust residues that still adhere to it, using pressurized air jets or high-pressure water jet application.

Disadvantages of the mechanical cleaning methods are the very great technological effort and the circumstance that as a result of the mechanical stress on the forming material, damage to the surface and to the structure as well as brittleness of the forming material occur.

A method in which the forming material covered with scale or rust layers is first sheathed with a closed layer of a lubricant, in a lubricant chamber, and subjected to forming that reduces its cross-section, in order to remove the layers, is also known (DE 10 2004 015 975 B3). This forming leads to the result that the scale layer comes loose from the forming material and breaks up into small layer parts, which are taken up by the lubricant sheath. The forming material treated in this way is subjected to precision cleaning immediately after it exits from the lubricant chamber, using rotating plastic brushes as well as a compressed-air blower. Afterward, a wire from which scale has been completely cleaned is present, for further processing in a downstream drawing process.

The invention is based on the task of developing a method and an apparatus with which coating of scale-covered, metallic, strand-shaped forming material with a solid lubricant, for forming in a downstream drawing process, is possible while avoiding the removal of scale layers or solid layers that contain scale and are present on metallic forming material. At the same time, the prerequisites for a significant improvement in the stability of the downstream drawing process and the quality of the products produced are supposed to be created.

This task is accomplished with the characteristics indicated in claims 1 and 6. Preferred embodiments are contained in the dependent claims.

In the method according to the invention, the scale-covered forming material is sheathed with a solid lubricant before the downstream drawing process, and formed at a forming degree ε of >3%, and afterward drawn through at least one accumulation chamber for mixing the scale particles that have formed from the scale layer, as the result of forming, with the lubricant present on the forming material after this forming.

For sheathing with the solid lubricant and for forming at a forming degree ε of >3%, the forming material is advantageously drawn through a lubricant-filled chamber, in which the solid lubricant is put under pressure. During forming, the brittle scale layer is loosened from the surface of the forming material as a result of the increase in size of the surface area that takes place on the forming material, and broken up into small scale particles.

In the dimensioning of the degree of forming, the amount of the degree of forming s should be selected to be so high, taking into consideration different material qualities, that it is sufficient to bring about complete loosening of the scale layer from the metallic matrix of the surface of the forming material, as the result of the increase in size of the surface area. However, the degree of forming s is not allowed to be selected to be too high, so that the scale layer loosened in this way is not pressed against the surface of the forming material again, in disadvantageous manner.

For mixing the resulting scale particles with the lubricant present on the forming material, the forming material is subsequently drawn through an accumulation chamber having an inside diameter that runs cylindrically or conically in the drawing direction.

Upon exit from the accumulation chamber, the forming material has a coating that does not have to be removed, but rather can be used as a high-performance lubricant film for a downstream drawing process. This lubricant film consists of the solid lubricant used in the pressure chamber and of scale particles embedded in it. The scale dust particles surprisingly improve the pressure and temperature stability of the lubricant film, in very decisive manner, and create the prerequisites for a significant improvement in the stability of the downstream drawing process and the quality of the products produced.

According to the invention, the pressure that prevails in the accumulation chamber, in the lubricant/scale particle mixture, is regulated.

It is practical if an accumulation chamber having an opening present at the discharge, to determine the desired thickness of the lubricant/scale particle film on the exiting forming material, is used. For the determination of the desired thickness of the lubricant/scale particle film on the exiting forming material, it is also possible to use a drawing plate.

To carry out the method, the invention includes an apparatus disposed on a drawing machine, the apparatus containing a device for sheathing a scale-covered forming material with a solid lubricant under the effect of pressure, and one or more downstream drawing plates for forming of the sheathed forming material at a forming degree ε of >3%, as well as a downstream accumulation chamber for mixing the scale particles that have formed from the scale layer as the result of forming with the lubricant that is present on the forming material after this forming.

According to the invention, the device for sheathing the scale-covered forming material with a solid lubricant and for forming at a forming degree ε of >3% is a lubricant-filled pressure chamber.

The accumulation chamber for mixing the scale particles that have formed from the scale layer as the result of forming with the lubricant that is present on the forming material after this forming has an inside diameter that runs cylindrically or conically in the drawing direction, according to the invention, wherein the inside diameter of the accumulation chamber that runs cylindrically is dimensioned to be >0.02 mm greater than the diameter of the forming material.

The accumulation chamber has an opening at its end, which opening determines the thickness of the lubricant/scale particle film desired on the exiting forming material. It is practical if this opening is implemented by means of a drawing plate having corresponding dimensions.

According to the invention, a device for regulation of the lubricant pressure that prevails in the accumulation chamber can be disposed on the accumulation chamber.

At its core, the invention contains a combination of technical measures for cleaning pretreatment of scale-covered forming material, using technical measures for coating such forming material for downstream forming. Advantageous synergistic effects are achieved with the combination, in that in the case of scale-covered forming material, it is possible to do entirely without a separate cleaning process for removing the scale, and, at the same time, a lubricant coating is achieved, which allows particularly high-performance forming processes as the result of its great pressure and temperature resistance.

In the following, the invention is explained in greater detail using an exemplary embodiment and a related drawing.

The apparatus shown in the drawing, for coating of a scale-covered forming material 1, contains a pressure chamber 2 (shown only in part), which is filled with a solid lubricant 3, which stands under a pressure P. The apparatus is disposed on a drawing machine not shown in the drawing, ahead of the drawing stages that serve for forming. The forming material 1 is drawn through the apparatus in the drawing direction Z. At the exit from the pressure chamber 2, a drawing plate 4 is disposed, with the forming material 1 is formed at a forming degree ε=5%. In this connection, the scale coat 5 that is situated on the forming material 1 is broken down into small scale particles and loosened from the metallic matrix of the forming material. The scale particles are transported, together with the lubricant on the forming material 1, into the accumulation chamber element 6 disposed downstream, which has a draw-through channel 7 that runs cylindrically, the inside diameter of which is 0.04 mm larger than the inside diameter of the forming material. Intensive mixing of the scale particles with the lubricant occurs in the draw-through channel 7 of the accumulation chamber element 6.

At the exit of the draw-through channel 7, another drawing plate 8 is disposed, which serves for determination of the coating thickness of the lubricant/scale particle film on the forming material 1, using its exit opening.

At its exit from the drawing plate 8, the forming material 1 has a coating 9 that does not need to be removed, but rather can be used as a high-performance lubricant film for a downstream drawing process. This lubricant film consists of the solid lubricant used in the pressure chamber and scale particles embedded in it. The scale particles surprisingly improve the pressure and temperature stability of the lubricant film, in very decisive manner, and create the prerequisites for a significant improvement in the stability of the downstream drawing process and the quality of the products produced. 

1. Method for coating of scale-covered, metallic, strand-shaped forming material with a lubricant, for forming during a downstream drawing process, wherein the scale-covered forming material is sheathed with a solid lubricant before the downstream drawing process, and formed at a forming degree ε of >3%, and afterward drawn through at least one accumulation chamber for mixing the scale particles that have formed from the scale layer, as the result of forming, with the lubricant present on the forming material after this forming.
 2. Method according to claim 1, wherein for sheathing with the solid lubricant and for forming at a forming degree ε of >3%, the scale-covered forming material is drawn through a lubricant-filled pressure chamber.
 3. Method according to claim 1, wherein for mixing of the scale particles that have formed from the scale layer as the result of forming with the lubricant present on the forming material, the forming material is drawn through an accumulation chamber having an inside diameter that runs cylindrically or conically in the draw-through direction.
 4. Method according to claim 3, wherein an accumulation chamber having an opening present at the discharge, which determines the thickness of the lubricant/scale particle film on the exiting forming material, is used.
 5. Method according to claim 3, wherein an accumulation chamber having a drawing plate present at the discharge, which determines the thickness of the lubricant/scale particle film on the exiting forming material, is used.
 6. Method according to claim 1, wherein the pressure that prevails in the accumulation chamber, in the lubricant/scale particle mixture, is regulated.
 7. Apparatus for coating of scale-covered, metallic, strand-shaped forming material with a lubricant, for forming during a downstream drawing process, containing, on a drawing machine, a device for sheathing a scale-covered forming material with a solid lubricant under the effect of pressure, and one or more downstream drawing plates for forming of the sheathed forming material at a forming degree ε of >3%, as well as a downstream accumulation chamber for mixing the scale particles that have formed from the scale layer as the result of forming with the lubricant that is present on the forming material after this forming.
 8. Apparatus according to claim 7, wherein the device for sheathing the scale-covered forming material with a solid lubricant and for forming at a forming degree ε of >3% is a lubricant-filled pressure chamber.
 9. Apparatus according to claim 7, wherein the accumulation chamber for mixing the scale particles that have formed from the scale layer as the result of forming with the lubricant present on the forming material after forming has an inside diameter that runs cylindrically or conically in the draw-through direction.
 10. Apparatus according to claim 7, wherein the inside diameter of the accumulation chamber that runs cylindrically is dimensioned to be >0.02 mm greater than the diameter of the forming material.
 11. Apparatus according to claim 7, wherein the accumulation chamber has an opening at its end, which opening determines the thickness of the lubricant/scale particle film desired on the exiting forming material.
 12. Apparatus according to claim 7, wherein the accumulation chamber has a drawing plate at its end, which plate determines the thickness of the lubricant/scale particle film desired on the exiting forming material.
 13. Apparatus according to claim 7, wherein a device for regulation of the lubricant pressure prevailing in the accumulation chamber is disposed on the accumulation chamber. 